1. Field of the Invention
The present invention relates to an off-road vehicle, and more particularly to a front-wheel suspension for an off-road vehicle.
2. Description of the Relevant Art
There are known three- and four-wheeled off-road vehicles known as buggies. Japanese Utility Model Publication No. 57-56890, for example, discloses an off-road vehicle having an engine mounted on a rear portion of a horizontal vehicle frame of pipes, a driver's seat disposed in front of the engine, and two front wheels rotatably mounted on a front portion of the vehicle frame by respective trailing-arm suspensions. When the driver is seated on the driver's seat the driver's legs are positionable in a front space of the vehicle frame FIG. 5 of the accompanying drawings fragmentarily shows a front portion of the vehicle frame of the disclosed off-road vehicle. A front wheel 51 is supported on the front portion of the vehicle frame 53 by a trailing arm 52.
Japanese Laid-Open Utility Model Publication No. 61-56185 shows a frame structure including a front portion having, on each lateral side, upper and lower parallel pipes extending longitudinally of the frame structure and inclined upwardly in the forward direction, with each front wheel being rotatably supported by a double-wishbone suspension comprising V-shaped upper and lower control arms pivotally mounted respectively on the upper and lower pipes. FIG. 6(a) illustrates such a V-shaped upper control arm 61 pivotally mounted on an upper pipe 62 of the frame structure. A V-shaped lower control arm (not shown) is disposed substantially below the V-shaped upper control arm 61.
With the trailing arm 52 (FIG. 5) being used to support the front wheel 51 on the frame 53, the distance f1 of the front end of the frame 53 to the center O of the axle of the front wheel 51, i.e., the amount of projection of the frame 53 forwardly of the axle of the front wheel 51, is large, and the weight of the frame is also increased. Since the frame 53 is disposed horizontally, the front end of the frame 53 may hit the ground while the vehicle is running over rough terrain.
According to the double-wishbone front wheel suspension shown in in FIG. 6(a), however, the amount of forward projection of the frame is reduced and so is the frame weight because the upper and lower pipes of the front end of the frame are included upwardly in the forward direction. The upwardly inclined upper and lower pipes are less liable to interfere with the ground while running over bumpy surfaces. The front and rear ends of the V-shaped upper and lower control arms are pivotally supported on the upper and lower pipes of the frame by front and rear pivot shafts. When the vehicle is viewed in side elevation, the distances from the vertical line passing through the center of the axle of each front wheel to the pivoted front ends of the upper and lower control arms are larger than or equal to the distances from the same vertical line to the pivoted rear ends of the upper and lower control arms. This suspension arrangement suffers the following problems:
Since the distances from the vertical line passing through the center of the axle of each front wheel to the pivoted front ends of the upper and lower control arms are comparatively large, much remains to be improved in avoiding undesirable physical contact between the upper and lower control arms and bumps on ground surfaces. Inasmuch as the distances from the vertical line to the pivoted rear ends of the upper and lower control arms are comparatively small, much remains to be improved in attaining rigidity against bending forces applied rearwardly to the upper and lower control arms.
In the suspension type shown in FIG. 6(a), a tie rod for turning the front wheel is required to extend between the parallel upper and lower pipes and project outwardly into coupled engagement with a knuckle arm. If brackets were mounted on the outer side surfaces of the upper and lower pipes and the front and rear ends of the upper and lower control arms were attached to the brackets by the pivot shafts, the tie rods would significantly interfere with the upper and lower pipes when the front wheels would be moved in large vertical strokes. As shown in FIGS. 6(a) and 6(b), a box-shaped floor panel 64 is disposed vertically from above the lower pipe 63 toward the upper pipe 62 for accommodating and protecting the legs L of the driver seated on the driver's seat. If the transverse length 1.sub.1 of the upper control arm 61 (and the lower control arm) is increased in order to increase the vertical stroke of the front wheels with the limited tread thereof, the upper pipe 62 must be disposed closely to the central line C of the vehicle frame. This however is disadvantageous in that the leg space for the driver is reduced as indicated by m.sub.1. If the leg space is increased as indicated by m.sub.2 as shown in FIG. 7(b) by spacing an upper pipe 62' widely from the vehicle frame central line C, the transverse length of an upper control arm 61' (and a lower control arm) is reduced as indicated by 1.sub.2 since the tread of the front wheels is limited, resulting in a reduced vertical stroke of the front wheels.